Cell-free lysates produced from amoebae of the genus Naegleria (including free-living strains of N. gruberi and pathogenic N. fowleri) have been found to contain an infectious agent capable of causing cytopathic response in secondary cultivations of chick embryo fibroblasts and human amnion cells. Research efforts will be directed toward: 1) study of this cytopathology employing electron microscopy as well as electron microscope autoradiography using lysate produced from radioactively-labeled amoebae, 2) use of such labeled cells and/or lysate prepared from N. fowleri amoebae to examine the effect of the infectious agent (or whole amoebae) on the central nervous system of inoculated mice, and 3) study of possible interactions involving the infectious agent between labeled and unlabeled Naegleria and other soil amoebae.